Nuclear fuel elements for a BWR (Boiling Water Reactor) have a tubular shape and have an inner space that comprises spacers, fuel rods, etc. In connection with maintenance and repair work in systems that are connected to the reactor tank, there is a risk that metal particles, flakes, fibers, etc. may be formed, which during subsequent operation can be transported by the reactor water to the reactor tank. Also during times when the reactor tank is opened, there is a risk that particles may fall down into the reactor tank. During a subsequent operation, such particles could then be circulated in the reactor tank with the reactor water. In order to capture such particles, filters are generally positioned at appropriate places where the reactor water passes. Small particles however, can become trapped inside the fuel elements and cause abrasion damage to sensitive parts such as the fuel rods. Particles that fasten to the insides of the fuel elements do not circulate with the reactor water and, therefore, they can not be captured by conventional filters.
The reactor water contains impurities derived mainly from corroded materials. When the reactor water during operation comes in contact with and is heated by the fuel rods, such impurities in the reactor water form deposits on the outer surfaces of the fuel rods. The deposits result in the reactor water experiencing an increased pressure drop in the fuel elements and a reduced heat exchange with the fuel rods.